Numerical analysis of utilizing the given blast basket exhaust cluster for small size ramjet testing

This paper describes compatibility assessment of testing a small ramjet combustor with nozzle exit diameter of 208 mm in the given exhaust cluster which has been originally developed for subsonic gas turbine testing. Exhaust hot gas for analysis has mass flow rate of 14.2 kg/s with nozzle inlet total pressure P _t = 7 bar and total temperature pressure T _t = 2000 K. The fixed exhaust cluster contains the dry augmentor tube of Φ1m x 5m length, the deflector cone, the blast basket, and the exhaust stack, the nozzle-to-augmentor spacing is about 1 m. By means of Computational Fluid Dynamics (CFD) analysis, it is shown that the whole flow field runs continuously to the outside environment without flow reversal and the whole structure’s surface temperature is less than 280°C, which is safe for its materials and installation of a periscope. It is found that by inserting the small primary augmentor tube in tandem between the engine nozzle and the fixed augmentor tube, secondary cooling flow is boosted 4% more, promoting lower structural temperature and more uniform flow in the exhaust stack. Since the primary augmentor shielded most of supersonic jet from the surrounding environment, near-field acoustics analysis is conducted to examine sound pressure level inside the test cell to compare different configurations. Results suggested that due to the primary augmentor presence, peak noise at low frequency hearing range could be reduced up to 20 dB.